Trash capture devices implemented into storm water drainage infrastructure have been around for decades. In the early 2000s cities in the Los Angeles, Calif. U.S.A. area started experimenting with what was come to be known as connector pipe screens, herein referred to generally as “CPS devices”. CPS devices were designed for installation inside storm water catch basins. CPS devices are made of perforated stainless steel or other related materials. The screens were placed around the outlet pipe of the catch basin to prevent trash from leaving the catch basin via the outlet pipe. Accumulated trash and debris could later be removed from the catch basin.
CPS devices have proven to be an effective and feasible way of preventing trash, organic matter such as leaves, and other debris from traveling through drainage infrastructure and exiting into the nation's oceans, lakes and streams where it causes damage to the environment. Unlike CPS devices known in the art, the presented invention is an innovative method and engineering of a connector pipe screen utilizing a single material to reduce costs, prevent waste material, increase strength and weight capacity, allows for easy assembly, and has a removable center piece to allow for jetting of the outlet pipe without removing the entire system.
In the early 2000s the EPA and California Regional Water Quality Boards issued what is known as a Total Maximum Daily Load (TMDL) for trash in the Los Angeles Region, specifically the Los Angeles River Watershed. Countless studies were conducted on the river and its discharge into the Pacific Ocean to measure the effectiveness of TMDL regulations. It was discovered that trash and debris entering the river basin from storm water infrastructure far exceeded acceptable levels. The trend to identify solutions to this problem were further promulgated by several environmental groups advocating for action to be taken to reduce the amount of trash discharged into the river and other watersheds.
Once TMDL standards were implemented, cities became accountable for what was exiting their storm water drainage infrastructure. Reduction benchmarks were mandated and over the coming years cities and counties would need to prove that the trash load leaving their storm water pipes and channels was decreasing. TMDL standards were come to be known as the LA Region Full Capture Trash TMDL. It was called Full Capture TMDL because the requirement stipulated that a device would have to remove 100 percent of trash and debris down to 5.0 mm in size at a specific flow rate equal to a 1-year, 1-hour storm prediction. It was determined this size storm could provide treatment of over 90 percent of the average annual rainfall. The 5.0 mm screen perforation size of a CPS device was chosen as a regulated size because 5.0 mm is slightly smaller than the size of a cigarette butt.
It is known in the art that the CPS device was originally invented by the City of Los Angeles. Several designs and configuration were tested and implemented. The designs initially started as flat horizontal screens. One problem discovered with the implementation of flat screens is the increased surface area subject to the direct flow of incoming water weakens the integrity of a CPS device with a flat screen as incoming water flow is not deflected against the curvature of a rounded screen. Later CPS devices became vertical screens of different shaped and sizes. Some were still flat, some were round, oval, L shaped, Z shaped, etc. The use of grated screens of any shape and varied materials are well-known in the art and have been integrated into storm water treatment systems for decades. Most of the designs use a perforated stainless steel screen mounted or welded to a frame of either solid flat bar or L metal to give the system strength and rigidity.
Generally, these CPS devices had to be low in cost to allow for widespread implementation. Commonly cities would issue project bids for several hundred devices at a time to be installed. Another challenge was how quickly these devices were required to be retrofitted into existing basins. The access into an already installed catch basin was typically at the curb opening face and through a standard 24-inch diameter manhole opening. A CPS device would have to fit through the narrow, existing openings as a singular unit; or have pieces which could fit through the catch basin opening. Once inserted, assembly was completed manually with screws, bolts and other mounting hardware and via welding.
To keep costs down some companies tried to minimize or eliminate the amount of framing material used. As the market became more competitive, the strength and performance of the CPS devices deteriorated, leading to structural failures due, in part, to the minimal framing material installed.
Another problem is that over time and between maintenance cleanings to empty the captured trash and debris, the CPS screen perforations common in the art can become obstructed and clogged by leaves and trash such as plastic bags. This blockage causes the water level behind the screen to build up to the top of the screen where trash and debris can override the designed purpose of the screen, flowing directly into a catch basin even during storms with low flows. Also, the weight of this water pressure can exert several hundred pounds of force. If the CPS device cannot handle the weight, the screen will likely collapse.
To address this problem, the County of Los Angeles implemented a new design requirement. The requirement was that the CPS device would need to be load tested and would have to withstand 60 pounds of force which the county representatives felt was sufficient for the majority of installations. Various commercial companies worked on designs which could meet the requirement without adding costs. There quickly became a need for an innovative design which could achieve the following. First, meet and exceed the 60-pound requirement. Second, meet this requirement while keeping costs down. Third, be modular in design so all the pieces could fit through the manhole opening. Fourth, have a removal middle section so city crews could still have easy access the CPS device to clean the pipes when needed.